They are yet another flavor of creature- obsessed with religion, loyal to their trine (also later Megatron a decent bit actually. Might depend on flavor), and desperate for a purpose :>
Best parallel in TF lore for them would very much be Sunstorm.
Seri is an Outlier, whose ability nearly killed them the first time it flared up. Their spark didn't account for the cold- constructed frame it was given, but after that scare incident, their mentor got them upgraded plating that can withstand their heat. Now they can dip in lava and be fine, much like Grimlock (don't toss em into the sun or something tho-). They don't exactly have a /radioactive/ spark like Sunstorm, their ability is very magma central. They can exert temperatures that can melt most materials; metal, rock, etc. Their power was controlled in the new frame they were given, and thus the energy is condensed to their servos and peds. Even so, it can empower their jets or firepower as well in short bursts. if they don't keep themselves in control to a certain degree tho, they could get hot enough to damage their own optics or melt themselves a bit. They had troubles when younger with literal meltdowns, but after moving on from their mentor to be with their trine, they still carry what they were taught when it comes to composure (as well as how they actually got their religious fanatics from their mentor lol).
Their trine mates are Codecracker/Soara and Levatair. Despite the tension regarding CC, they do still are quite forgiving of her behavior. The main thing Seri doesn't like is when CC disrespects their Trine Leader, so they do step in occasionally to defuse things.
When it comes to the start of the war, Seri was absolutely appalled at Sentinel betraying the true Primes, and absolutely rooted for Megatron ripping the guy in half as divine retribution. (I will note that ngl I am not sure of one solid continuity, tho that's a clear event when also thinking of another one of my characters I have in mind.) Seriph admired Megatron's strength and sense of justice, and their perspective of that was rather warped from what they wanted to interpret it as. They followed Megatron with all the other seekers, but was unsure about the Optimus Prime factor. Primus had chosen Orion, and given him the matrix; but Seriph believes that OP is misguided and misunderstood the responsibility given to him (ultimately, OP would be basically the only one to be able to convince them to change tho ngl). Instead as they plunge into war, Seriph believes it is the era of the next purge like The Flood in Christian shit. They believe it's their duty to reduce all those who stand against their promised new world to ash and molton slag. Despite the fact that they are a brutal killer, they do feel some level of sympathy for those they feel were misguided, and often will give a short prayer before sending them to the Allspark. although there are some they come across that they only give silence if they believe that person belongs to the Pit. They view death as more of a reset button for those who deserve a second chance in the new world. Under the impression that after the storm has settled, they truly will be able to rebuild it better from the carnage.
Theyre believe of frames being fleeting, and replaceable, definitely stem from their cold-construct background; as well from the fact they they had needed to be rebuilt when they barely survived. (that instance is what instilled their deep seeded belief that Primus allowed them to remain for a /reason/)
Seriph's fighting style is very close combat oriented. They often will catapult themself at the enemy and wrestle their opponents with their fired servos and the mini wings on their arms that are used like the blades Arcee has in TFP. They even more often use their blasters at close range, although they still can use em at a distance. The 6 turrets they have are faced down in flight, so they operate more so like a bomber.